606 



Mr. J. B. Jukes and the Rev. Samuel Haughton on the 



the felspar of the Three Rock Mountain, soda in excess of potash in the 

 proportion of 6 : 5. I place most reliance on the numbers contained in 

 Table IX.:— 



Table IX. 



Calculated Felspar of Granite Rock. 



This Table gives the composition of the felspar of the entire rock, -which is 

 a tersilicated felspar, composed partly of orthoclase, and partly of a confused 

 paste, the composition of -which cannot be ascertained by experiment, in con- 

 sequence of the impossibility of separating the orthoclase from it. 



The result of the preceding calculations, so far as they relate to the minera- 

 logical composition of the granite, is as follows: — 



Table X. 

 Mineralogical Analysis of Granite. 



The preceding result is, I believe, very accurate, and is, so far as I know, 

 the first exact representation of the composition of a quaternary granite. The 

 granite of Leinster is well suited for a calculation such as I have made, as it 



